1. Field of Invention
The present invention relates to a process for the atom transfer polymerization of olefinically unsaturated monomers in which molecular weight control is achieved by the presence of certain transition metals, especially copper, and diimine complexes.
2. Description of Related Art
It is desirable to be able to produce high molecular weight polymers with a low molecular weight distribution by catalyzed addition polymerization, in particular of vinylic monomers. Hitherto, this has been achieved by polymerizing via ionic processes typically in the presence of organometallics such as alkyl lithiums that are sensitive when reacted with water and other protic species. Therefore, monomers containing functional groups are not readily polymerized. The use of ionic systems also precludes the use of solvents that contain protic groups and/or impurities resulting in very stringent reaction conditions and reagent purity being employed.
More recently, radical polymerization systems based on the combination of a transition metal halide and an alkyl halide have been used. For example, Matyjasewski (Macromolecules (1995), vol. 28, pages 7901-7910 and W096/30421) describes the use of CuX (where X=Cl, Br) in conjunction with bipyridine and an alkyl halide to give polymers of narrow molecular weight distribution and controlled molecular weight. This system suffers from the disadvantage that the copper catalyst is only partially soluble in the system and thus a heterogeneous polymerization ensues. The level of catalyst that is active in solution is thus difficult to determine. Percec (Macromolecules, (1995), vol. 28, page 1995) has extended Matyjasewski's work by using arenesulphonyl chlorides to replace alkyl chlorides, again this results in heterogeneous polymerization. Sawamoto (Macromolecules, (1995), vol. 28, page 1721 and Macromolecules, (1997), vol. 30, page 2244) has also used a ruthenium based system for similar polymerization of methacrylates. This system requires activation of monomer by aluminum alkyl, itself sensitive to reaction with protic species which is an inherent disadvantage. These systems have been described as proceeding via a free radical mechanism that suffers from the problem that the rate of termination is &gt;0 due to normal radical-radical combination and disproportionation.